1. Field of the Invention
The present invention relates to a mobile station for transmitting a retransmission packet corresponding to a transmission packet to a base station according to a synchronous retransmission control scheme in single-carrier FDMA (Frequency Division Multiple Access) radio access. The present invention also relates to a base station for transmitting a control signal to the mobile station.
In addition, the present invention relates to a base station for transmitting a retransmission packet corresponding to a transmission packet to a mobile station in multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) radio access.
2. Description of the Related Art
Retransmission control schemes are used in radio communication systems, in which an error in a packet transmitted between a base station and a mobile station is detected and only a packet with the error is retransmitted. Regarding retransmission timings, retransmission control is classified into two schemes as shown in FIG. One scheme is referred to as Synchronous ARQ (automatic repeat request) and the other scheme is referred to as Asynchronous ARQ.
According to Synchronous ARQ, packets are retransmitted at predetermined retransmission timings. For example, when a transmission packet at a timing #0 (S00) is detected as an error packet, the corresponding retransmission packets can be transmitted at timings #0 (S10 and S20). In other words, retransmissions are performed at frames which are integral multiples of RTT (Round Trip Time) or control loop delay.
According to Asynchronous ARQ, packets are retransmitted at any timing after one RTT. For example, when a transmission packet at a timing #0 (A00) is detected as an error packet, the corresponding retransmission packets can be transmitted at any TTI (Transmission Time Interval) after A10. In other words, retransmissions are performed at any TTI (A10-A25) after one RTT from the transmission packet.
Regarding the format for the retransmission packet, the retransmission control is also classified into two schemes. One scheme is referred to as Non-adaptive ARQ and the other scheme is referred to as Adaptive ARQ.
According to Non-Adaptive ARQ, a retransmission packet is transmitted with the same format as an initial transmission packet. For example, when the initial transmission packet is transmitted with a channel coding rate (R) of ½ and a data modulation scheme of QPSK, the retransmission packet is transmitted with the same channel coding rate (R=½) and the same data modulation scheme (QPSK).
According to Adaptive ARQ, the retransmission packet is transmitted with a different format from the initial transmission packet. For example, when the initial transmission packet is transmitted with a channel coding rate (R) of ½ and a data modulation scheme of QPSK, the retransmission packet is transmitted with a different channel coding rate (R=⅓) and a different data modulation scheme (BPSK).
The combination of Asynchronous ARQ and Adaptive ARQ is used in HSDPA (High Speed Downlink Packet Access), which is a downlink high speed packet transmission technology for WCDMA (Wideband Code Division Multiple Access) (see 3GPP TS 25.212, “Multiplexing and channel coding (FDD)”, for example).
The combination of Synchronous ARQ and Non-adaptive ARQ is used in Enhanced Uplink, which is an uplink high speed packet transmission technology for WCDMA (see 3GPP TS25.309, “FDD enhanced uplink; Overall description; Stage 2”, for example).
According to typical WCDMA, a frequency bandwidth allocated to each user is fixed (always 5 MHz). Thus, a retransmission packet is transmitted with the same frequency bandwidth as a transmission packet. Accordingly, when the frequency bandwidth has strong interference from neighbor cells, it is expected that the retransmission packet will be of poor reception quality.